Secondary ion mass spectrometry

Investigating the surface chemistry of samples

Secondary ion mass spectrometry is a highly sensitive technique for investigating the surface chemistry of samples. A focused “primary” ion beam sputters atomic, molecular and molecular fragment “secondary” ions characteristic of the sample surface chemistry. These secondary ions are subsequently extracted into a mass analyser where they are separated, identified and detected according to their mass to charge ratio. Removal of sample material with the primary ion beam, commonly a large gas cluster, facilitates depth profiling and 3D imaging. The SIMS technique provides:

• Identification of trace elements, organic molecules and polymers on surfaces, with better than 1 ppm sensitivity for some molecules and ppb sensitivity for some elements
• Surface chemical imaging with 100 nm – 5 µm spatial resolution
• Extremely surface sensitive information from top 1 nm of sample in static SIMS mode
• 3D elemental / molecular distribution with better than 50 nm depth resolution in depth profiling mode

NPL has extensive experience in the development and application of SIMS for analysis of diverse organic and biological materials. Ongoing research has developed fundamental understanding of depth profiling of organic materials, and of matrix effects, which can alter secondary ion yields over several orders of magnitude and hinder quantification.

SIMS is well suited for imaging of biological materials, advanced inorganic and organic materials as well as samples from other fields of research. The depth profiling capability of gas cluster ion beams enables efficient depth profiling and 3D imaging of thin layered structures, such as those commonly found in semiconductor and optical devices and advanced manufactured products. Applications include the characterisation of interfacial chemistry in organic LED displays, imaging of conditioning products in hair and sub-cellular localisation of drugs.

Sputter yield values

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